1. Field of the Invention
The present invention generally relates to a power supply IC having a plurality of power supply circuits, and particularly relates to a power supply IC having a series regulator for supplying power to high-frequency circuits and, a switching regulator. The invention also relates to a communication apparatus in which such a power supply IC is employed.
2. Description of the Related Art
The operating voltage of logic circuits such as CPUs and DSPs has dropped, from 2.5 V to 1.8 V or to 1.5 V, for example, in line with the development of portable equipment that requires low power consumption. There is a continuing trend toward a lower operating voltage. For the purpose of supplying power to an IC that requires a low-voltage operation, a switching regulator is considered more suitable than a conventional series regulator due to its high efficiency. There is also a strong need for the miniaturization of portable equipment. An analog circuit including a power supply unit, which is conventionally provided as a separate chip, is now integrated into one chip to achieve such miniaturization.
In communication apparatus such as cellular phones, however, a switching regulator that functions as a noise source needs to be provided as a separate chip, separate from a power supply unit of the RF circuit that suffers trouble if affected by high-frequency noise. There should be provided some distance between these chips on the printed circuit board, or a filter should be provided between the chips, as a counter measure against the noise.
In order to obviate the problems as described above, there is a need for a power supply IC in which a switching regulator generating high-frequency noise and a series regulator for RF circuits are provided on a single chip, and also a need for a communication apparatus in which such a power supply IC is employed.